(1) FIELD OF THE INVENTION
The present invention relates to novel amino alkane diphosphonic acids and more particularly to novel N-hydroxy alkane amino alkane diphosphonic acids and their alkali metal salts, to a process of making said compounds, to compositions containing them, and to a method of using such compositions.
(2) DESCRIPTION OF THE PRIOR ART
Only a limited number of hydroxy amino phosphonic acids are known at present. For instance, German Pat. No. 1,214,229 describes, among others, the production of mono-ethanolamino or, respectively, di-ethanolamino (methyl phosphonic acids). These compounds are produced by phosphono-methylating mono-ethanolamine or, respectively, di-ethanolamine by means of phosphorous acid and formaldehyde. Hydroxy amino (methyl phosphonic acids) in which one or two methylene phosphonic acid groups (--CH.sub.2 PO.sub.3 H.sub.2) are attached to the nitrogen atom, are obtained according to the process of said patent.
German Published Application (Auslegeschrift) No. 2,130,794 relates to a process of producing 1-hydroxy-3-amino propane-1,1-diphosphonic acid by reacting .beta.-alanine with phosphorus trichloride and phosphorous acid. The resulting reaction product is a hydroxy amino diphosphonic acid in which no substituent is attached to the amino group, while the hydroxyl group is attached to the same carbon.
An object of the present invention is to provide a method of using N-hyroxy alkane amino alkane diphosphonic acids for complex formation and sequestering effects in aqueous media.
Another object of the present invention is to provide a method of using N-hydroxy alkane amino alkane diphosphonic acids for suppressing scale and corrosion in an aqueous medium used for the heat treatment of containers.
Other objects of the present invention will become apparent as the description proceeds.
In principle the novel N-hydroxy alkane amino alkane diphosphonic acids according to the present invention are represented by the following formula ##STR1## In said formula
R is hydrogen, lower alkyl, especially methyl or ethyl; aryl, especially phenyl; hydroxy alkyl, especially hydroxy ethyl; or carboxy alkyl, especially carboxy methyl;
R.sub.1 is hydrogen; lower alkyl, especially methyl; hydroxy alkyl, especially hydroxy alkyl of the formula C.sub.n H.sub.2n OH; the propylene glycol group of the formula C.sub.3 H.sub.7 O.sub.2 ; or the hydroxy propionic acid group of the formula C.sub.3 H.sub.5 O.sub.3 ; and
R.sub.2 is hydroxy alkyl, especially hydroxy alkyl of the formula C.sub.n H.sub.2n OH;
n in said hydroxy alkyl group is a numeral from 2 and 3.
It is evident that the novel phosphonic acids according to the present invention differ from the known hydroxy amino phosphonic acids disclosed in the above mentioned German Patent and German Published Application by the feature that geminate phosphonic acid groups are present at the C.sub.1 -atom. In contrast to the 1-hydroxy-3-amino propane-1,1-diphosphonic acid disclosed in German Published Application No. 2,130,794 the substituents carrying the hydroxyl groups are attached to the nitrogen atom of the amino group while, according to said German Published Application, the amino group is not substituted.
The phosphonic acids according to the present invention or their alkali metal salts are preferably obtained by reacting amino alkane diphosphonic acids with one or two hydrogen atoms at their nitrogen atom with three- and four-membered cyclic ethers. Suitable cyclic ethers are, for instance, ethylene oxide, propylene oxide, trimethylene oxide, glycidol and its ethers, epichlorohydrin, glycidic acid and its esters and amides, .beta.-methyl glycidic acid and its esters and amides, and the like cyclic ethers.
Especially suitable phosphonic acids starting materials are amino lower alkane diphosphonic acids having up to four carbon atoms in the alkane chain and also amino aryl alkane diphosphonic acids. Examples of such phosphonic acids are, for instance, amino methane diphosphonic acid, amino ethane diphosphonic acid, 2-carboxy-1-amino ethane-1,1-diphosphonic acid, benzylamino diphosphonic acid, 1-amino propane-1,1-diphosphonic acid, and the like.
The reaction components, i.e. the amino alkane phosphonic acids and the cyclic ethers, are advantageously reacted in the proportion of 1 : 1 to 1 : 1.5, if only one replaceable hydrogen atom is attached to the nitrogen atom, or in the proportion of 1 : 2 to 1 : 3, if both hydrogen atoms of the amino group of the starting phosphonic acid can be replaced.
Preferably the sodium and potassium salts of the starting phosphonic acids are used in the reaction. The free amino phosphonic acids themselves, however, can also be used under certain conditions, although the preferred procedure is to use the alkali metal salts in the reaction. When using the free acids, it is the preferred procedure to carry out the reaction in the presence of an alkali metal hydroxide.
The resulting new phosphonic acids are distinguished over known phosphonic acids by being readily prepared in a good yield and by being of a water-solubility that can be considered as excellent for most uses. The new phosphonic acids are highly effective agents for yielding complex compounds with divalent and polyvalent metal ions. They can be employed advantageously in all those instances in which a high sequestering power is required.
The novel phosphonic acids according to the present invention have proved to be especially valuable, because they are highly stable against hydrolysis even at a high temperature. Thus they can be employed in all those processes in which the temperature exceeds 100.degree. C. and they can be used in all aqueous media in which the hardness-forming agents in the water have a disturbing or detrimental effect or in which the action of polyvalent metal ions is to be excluded.
The new phosphonic acids have proved to be of value for stabilizing the hardness in aqueous media even in substoichiometric amounts, i.e. in so-called threshold treatment.
A further possible use of the compounds according to the present invention is their use for producing liquid fertilizer preparations.
Of special importance is the exceptionally high solubility of the free acids in aqueous media. The solubility of most of the heretofore known amino phosphonic acids is much lower. For instance, the compounds described in the following examples have a solubility of at least 100 g. in 100 cc. of water.
In contrast to the extraordinarily high solubility of the novel N-substituted amino alkane phosphonic acids, the known unsubstituted amino alkane phosphonic acids have only a low solubility in water. The solubility of the following known amino phosphonic acids in water at 25.degree. C. is, for instance, as follows:
Amino methane diphosphonic acid: 0.3%
1-Amino ethane-1,1-diphosphonic acid: 3.4%
Ethylene diamino tetramethylene phosphonic acid: 2.3%
Hexamethylene diamino tetramethylene phosphonic acid: 0.8%
It is interesting to note that the solubility of the phosphonic acids according to the present invention is even increased by the presence of small amounts of impurities, especially those present already in the starting materials and remaining in the novel amino phosphonic acids during their preparation.